<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>盒子模型</title>
    <style>
        body {
            margin: 0;
            padding: 0 50px;
        }
        .box {
            display: block;
            width: 150px;
            height: 50px;
            padding: 50px;
            border: 50px solid #ff0000;
            margin: 50px;
        }
        .classdiv {
            width: 50px;
            height: 50px;
            background-color: #000000;
        }
    </style>
</head>
<body>
    
    <span class="box">盒子内部的内容</span>
    <div class="classdiv"></div>
</body>
</html>